Impact molding of galvanic cell cathodes



Nov. 10, 1964 L. c. HOSFIELD IMPACT MOLDING 0F GALVANIC CELL CATHODESFiled Oct. 16, 1961 INVENTOR.

LEE C. HOSFIELD ATTORNL/Y United States Patent 3,156,749 IMPACT MOLDING0F GALVANIC CELL CATHODES Lee C. Hosfield, Sarasota, Fla., assignor toUnion Carbide Corporation, a corporation of New York Filed Oct. 16,1961, Ser. No. 145,325 3 Claims. (Cl. 264-161) This invention relates toan improved process for molding cathodes for use in electrochemicalcells and to apparatus suitable for performing such a process.

In certain type cylindrical galvanic cells such as alkaline-manganesedioxide-zinc cells and Leclanch cells of the type which are referred toas inside out cells (US. Patent 2,605,299, I. P. Teas, July 29, 1952), acylinder of mix is provided in juxtaposition with the inside of the cellcontainer. This cylinder serves as the cathode or current collector inthe cell reaction and must be compressed tightly to minimize internalresistance.

These type cathodes are currently being produced by one of two methods.The cathodes in alkaline cells are conventionally provided bycompression molding of a preform of cathodic mix comprising manganesedioxide and graphite in the cell container, followed by a despruing orremoval of the compressed mix in the center of the preform. This methodis not completely satisfactory due to the rapid wear which isencountered on the high pressure hydraulic equipment that it used toapply the pressure. In addition, the tools which are employed to performthe de-spruing operation are expensive and wear rapidly on the somewhatabrasive cathodic mix.

The cathode or current collector in the Leclanch cell of the typedescribed is composed of a cylinder of graphite and wax which is injuxtaposition with the inside of a paper spiral wound tube which formsthe cell jacket. The common method now in use to form such cathodesconsists of injection molding them in large presses which are providedwith necessary heating and cooling cycles. It will be appreciated thatthe time cycle of such equipment is controlled by the fact that theformed cathode must be allowed to cool to a temperature at which it willnot distort or sag when it is removed from the press.

The principal object of the invention is to provide a process forforming cylindrical cathodes which avoid the above disadvantages of theprior art.

Another object of the subject invention is to provide a process forforming cylindrical cathodes quickly and efficiently and which may becarried out in simplified equipment.

Broadly stated, the objects of the invention are accom plished by impactmolding of a cylindrical cathode mix in place within a cylindricalgalvanic cell container. utilizing a fluted molding punch as the moldingforce.

The invention will be more readily understood by reference to theaccompanying drawing wherein the single figure is a front elevationpartially in section, of a punch 7 press suitable for carrying out theprocess of the invention, and which shows a fluted punch within acylindrical cell container in the process of forming a cathode.

More specifically, the process of the invention con1 prises driving apunch into a cell container into which more cathodic mix than isrequired to form the cathode of the particular cell, has been deposited.The excess cathodic mix is forced out of the cell container by means ofa plurality of flutes on the side of the punch. In the preferredembodiment at least three flutes should be provided, and best resultshave been obtained with six flutes.

After the expulsion of the excess cathodic mix, and prior.

3,156,749 Patented Nov. 10, 1964 punch also smoothes over the innersurface of the molded cathode.

Referring now to the drawing, a cell container 10 is shown in positionin a cavity 11 in a base 12 of a punch press 14. The cell container 10resides on an ejector member 16 which is used to remove the container 10from the cavity 11 after the cathode 18 is formed. In the process of theinvention, a punch 20 which is provided with a plurality of flutes 21and which is part of the upper por tion 22 of the punch press 14 isdriven into a partially precompressed cathodic mix or into a pluralityof pellets made from the cathodic mix the punch '20 having a diametersmaller than the inside diameter of the cell container 10. In order toinsure against poor cathode molding due to entrapment of air in thecathode, the density of the mix or pellets should be at least 2.2 gramsper cubic centimeters. This action forms the cathode 18 into the desiredshape which is controlled by the space defined by the fluted punch 20and the walls of the punch cavity 11. As can be seen from the drawing,the excess cathodic mix will be ejected from the cavity 11 by means ofthe flutes 21 which extend above the cavity 11. A stripper ring 24retains the cathode 18 in place while the punch 20 is being withdrawn.In the preferred embodiment a force rotating eccentric cam 26 isprovided which will rotate the punch from about 5 to 30, 15 beingpreferred, to break the adhesive force between the punch 20 and thecathode 18, before the punch 20 is withdrawn. The rotation takes placewhen the upper portion 22 of the punch press 14 starts the upstroke andwhile the punch 20 is held in the down position by a spring 28 until theslack is taken up in a linkage 30. This rotation of the punch 20 alsoirons over the rough places on the inner wall of the cathode 18 alongwhere the excess cathodic mix was ejected by means of the flutes 21.

As an example of the invention, G size alkalinemanganese dioxide-zinccells were made with cathodes formed by the impact molding processdisclosed. A G size cell is defined in circular C 466 of the NationalBureau of Standards of the United States Department of Commerce. Thecells so produced gave 48 cycles to .9 volt on the 1.125 ohm 4 hourdischarge, 500 milliamp, 10 hour charge cycle. Cells of the identicalsize with cathodes producedby the conventional molding techniquedescribed, gave only 43 cycles when subjected to the same test.

Leclanch cathodes formed by impact molding also compared favorably withthe conventionally prepared Leclanch cathodes when compared on aresistance basis. The cathodes were immersed in mercury and theresistance was read through the cap on bridge. The resistance values ofthe cathodes'of the invention varied from .060 to .110 ohm per linearinch while the range for the injection molded prior art cathodes wasfrom .095 to .126 ohm per linear inch. The lower resistance for thecathodes of the invention is indicative of the high density which isachieved by the process of the invention.

The process and apparatus of the invention has proved successful in thecontrol of the amount of material in the cathode formed by the moldingoperation. In a trial of 49, /2 D size alkaline cells, the amount ofcathodic mix added to the cell container was varied between 26 and 34grams. The weight of the molded cathode after being formed by the flutedpunch varied only from 24.33 to 26.04 grams, thus demonstrating that adesired final cathode weight can be obtained even though a substantialvari- I bottom of said cell container; driving a cylindrical punch,smaller in diameter than the inside diameter of said cell container andprovided with a plurality of flutes for expelling said excess of saidcathodic mix from said container, into said cathodic mix, removing saidexcess of said cathodic mix through said flutes while the remainder ofsaid cathodic mix is molded into a cathode between said punch and theinner walls of said cell container, rotating said punch a slight amountprior to withdrawal from said container whereby said excess of saidcathodic mix in said flutes is sheared and severed off from said formedcathode; and then removing said punch from said cell container thusforming a finished cathode-container structure.

2. The process of claim 1 wherein said punch is rotated betweenapproximately 5 and 30.

3. An apparatus suitable for impact molding a cylindrical cathode inplace in a cylindrical container containing an excess of cathodic mixtherein, which comprises, a punch press, said punch press comprising amovable upper portion having a cylindrical punch provided with aplurality of flutes for expelling said excess of said cathodic mix fromsaid cylindrical container, a stationary lower portion provided with acavity for receiving said cylindrical container containing said excessof cathodic mix which is in line with said fluted punch, a cam having anoblique slot for controlling the rotation of said fluted punch,resilient means urging said fluted punch downwardly, means for movingsaid fluted punch in and out of said cavity, said fiutes of said punchextending above said cavity when said punch is within said cavity, and acam pin rigidly attached to said movable upper portion of said presswhich rides in said oblique slot of said cam, whereby said punch rotatesfrom about 5 to about prior to the initial withdrawal of said punch fromsaid cavity and whereby said excess of said cathodic mix in said flutesis sheared and severed off from said formed cathodecontainer structure.

References Cited in the file of this patent UNITED STATES PATENTS1,195,118 Weida Aug. 15, 1916 1,412,962 Perrault et al Apr. 18, 19221,585,643 Bello May 25, 1926 2,027,483 Keller Jan. 14, 1936 2,040,674Severance et al. May 12, 1936 2,359,674 Pollods Oct. 3, 1944 2,561,735Haller July 24, 1951 2,659,132 Leontes et al. Nov. 17, 1953 2,767,438Pingel Oct. 23, 1956 2,987,775 Albrecht et a1 June 13, 1961 3,053,713Juras Sept. 11, 1962 FOREIGN PATENTS 505,815 Italy Dec. 18, 1954

1. A PROCESS FOR IMPACT MOLDING A CYLINDRICAL CATHODE IN PLACE IN AGALVANIC CELLCONTAINER WHICH COMPRISES THE STEPS OF DISPENSING AN EXCESSFO CATHODIC MIX INTO THE BOTTOM OF SAID CELL CONTAINER; DRIVINGACYLINDRICAL PUNCH, SMALLER IN DIAMETER THAN THE INSIDE DIAMETER OF SAIDCELL CONTAINER AND PROVIDED WITH A PLURALITY OF FLUTES FOR EXPELLINGSAID EXCESS OF SAID CATHODIC MIX FROMSAID CONTAINER, INTO SAID CATHODICMIX, REMOVING SAID EXCESS OF SAID CATHODIC MIX THROUGH SAID FLUTES WHILETHE REMAINDER OF SAID CATHODIC MIS IS MOLDED INTO A CATHODE BETWEEN SAIDPUNCH AND THE INNER WALLS OF SAID CELL CONTAINER, ROTATING SAID PUNCH ASLIGHT AMOUNT PRIOR TO WITHDRAWAL FROM SAID CONTAINER WHEREBY SAIDEXCESS OF SAID CATHODIC MIX IN SAID FLUTES IS SHEARED AND SEVERED OFFFROM SAID FORMED CATHODE; AND THEN REMOVING SAID PUNCH FROM SAID CELLCONTAINER THUS FORMING A FINISHED CATHODE-CONTAINER STRUCTURE.